The present invention relates to a method for the polymerization of olefinic hydrocarbons and the production of a complex-initiator therefor. In a more specific aspect, the present invention relates to a method for the polymerization of conjugated dienes alone or in admixture with other conjugated dienes or vinyl-substituted aromatics and the production of a complex-initiator therefor. In a still more specific aspect, the present invention relates to the polymerization of butadiene alone or in admixture with other conjugated dienes or vinyl-substituted aromatic hydrocarbons. In an even more specific aspect, the present invention relates to a method for the polymerization of butadiene to produce liquid polymers having one phenyl group per butadiene polymer chain which are suitable for use as lubricants, upon hydrogenation thereof.
A number of processes for the polymerization of olefinic hydrocarbons to produce products varying from solid polymers of high molecular weight to liquid polymers of lower molecular weights are known in the art. However, the most frequently utilized process is the anionic polymerization of olefins. Anionic polymerization can be utilized in the polymerization of numerous olefinic hydrocarbons. However, most frequently utilized olefins are conjugated dienes, particularly butadiene, alone or in admixture with other conjugated dienes or vinyl substituted aromatic hydrocarbons. This is in spite of the fact that butadiene is one of the most difficult monomers to polymerize by this technique.
Anionic polymerization involves two basic steps. The first step includes metallation or initiation of the monomeric olefin by an organometallic compound, usually an alkali metal initiator or catalyst together with the polymerization of the olefin to produce a "living polymer", which continues to grow until polymerization or chain elongation is terminated. Therefore, the second step involves termination of the polymerization or chain elongation by utilization of all of the monomer or transmetallation or chain transfer of the initiator to another molecule to form another compound or both. Since the reaction is highly exothermic and the initiators and transmetallation agents are usually not soluble in a monomer, a solvent is utilized throughout the process. Accordingly, in many cases, the transmetallation step involves transfer of the initiator to the solvent material. In addition, by the utilization of selected solvents, such as alkyl-substituted aromatic hydrocarbon solvents, it is possible to produce polymers having one or more units of the solvent attached to the monomer chain.
The major problem in anionic polymerization is the fact that the two basic steps are quite difficult to separate, since transmetallation begins to take place shortly after metallation and polymerization begin and there is a tendency for the transmetallation to occur faster than the metallation, once the process has begun. This, of course, leads to difficulty in controlling the character of the product, both as to the molecular weight and the molecular weight distribution. Numerous solutions to this problem have been proposed. For example, it is known that, if the catalyst to monomer ratio is low, high molecular weight solid polymers are produced. On the other hand, if the catalyst to monomer ratio is increased, the molecular weight of the product is decreased, thus making it possible to produce lower molecular weight liquid polymers. Thus control of the catalyst to monomer ratio has been proposed as one solution. However, the catalysts or initiators are one of the primary cost factors in the process. It has also been shown in the prior art that the utilization of certain organolithium initiators or catalysts make the initiation-polymerization reaction faster and thus prevent premature transmetallation. However, the organolithium initiators or catalysts are the most expensive of this group of materials. It has also been shown in the prior art that the amount of catalyst utilized to obtain optimum results can be reduced by proper selection of solvents or diluents and their volume. It is also known in the art that, at comparatively low temperatures, the transmetallation or chain transfer reaction becomes fast. Accordingly, an obvious solution would be to increase the temperature. However, if the temperature is too high, the chain transfer or transmetallation reaction takes place too slowly to be practical. Accordingly, in order to control the character of the product as well as the yield of desired product, it is necessary to precisely control the temperature. As previously pointed out, the process is exothermic, thus exaggerating problems of temperature control. Techniques suggested in the prior art include disposition of cooling coils in the reaction medium, the utilization of cooling baths about the reactors and the utilization of cooling jackets on the reactors. While these techniques are effective on a laboratory scale operation, they obviously leave much to be desired in large commercial scale operations. As previously pointed out, some moderation of control of the temperature can be attained by the utilization of solvents throughout the process.
It is also obvious from the above that the rates of the competing reactions are greatly affected by the mixing of the reactants. In short, it is obvious that the rates of reaction and thus the character of the products and yield of desired product require contact of the proper reactants, in the proper volumes and at the proper times. The character of the mixing is of course dependent upon the manner of contact of the reaction materials. The prior art has taught a number of batch, semi-continuous and continuous techniques. These techniques have generally been selected in order to control the rates of reaction and, to the extent possible, separate the two steps of the reaction. One proposal involves the incremental addition of monomer to a solvent solution of the initiator or catalyst and one or more chain transfer or transmetallation components. In this technique, each incremental addition of monomer is followed by a sufficient residence time to permit complete conversion of all of the monomer to a living polymer, followed by transmetallation of the metal of the initiator from the living polymer to the solvent material. This technique can be practiced in batch, semi-continuous or continuous operations. A semi-continuous technique which has also been proposed involves the continuous addition of gaseous monomer to a solvent solution of initiator and product which is continuously cycled from the reactor to a product collection pot and back to the reactor where it contacts the gaseous monomer. In this process, it is stated that initiation takes place in the product pot, chain elongation in the reactor and transmetallation in the transport line from the reactor to the product pot. When a sufficient amount of product is obtained, the operation is terminated to recover product. Constant temperature baths are utilized for both the reactor and the product pot. A continuous adaptation of this technique involves preheating a solvent solution of initiator or catalyst and transmetallation or chain transfer agents and continuously passing the solution through a plurality of reactors, in sequence, in which gaseous monomer is added to each of the reactors continuously. This technique thus involves initiation in the preheater, chain elongation or polymerization in the reactors and transmetallation or chain transfer in the transport lines between the reactors and from the last reactor to the product collection means. Yet another technique involves premixing of monomer and initiator, introducing the mixture into a dual screw conveyor or extruder, introducing a "stopper or stabilizer" at an intermediate point along the extruder and granulating the resultant solid polymer. It is stated that the primary purpose of this technique is to avoid the use of solvents. Temperature control is maintained by a cooling or heating jacket about the extruder. Some of these manipulative techniques create additional problems. For example, batch operations are inherently more expensive than semi-continuous or continuous, they produce broader molecular weight distributions due to poor mixing, the poor mixing, together with the utilization of cooling coils, cooling baths and cooling jackets, results in poor heat transfer and it is most difficult to carry out any type of recycle of product or reactants. The techniques utilizing monomer in the gaseous form also have the inherent disadvantages of inefficient mixing, inefficient heat transfer, high energy costs for the introduction of gaseous monomer, and the utilization of large amounts of expensive initiators or catalysts. The extruder reactor technique, while saving on solvent, obviously results in the added expense of preliminary mixing, poor temperature control and complete loss of expensive initiators or catalysts as well as the unspecified "stopper or stabilizer" material. It is also, of course, impossible in this process to produce liquid polymers.